linux-kernel - Re: pte_offset_map for ppc assumes HIGHPTE

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Message-Id: <1185405765.5439.371.camel@localhost.localdomain>
Date:	Thu, 26 Jul 2007 09:22:45 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Andreas Schwab <schwab@...e.de>
Cc:	Satya <satyakiran@...il.com>, linuxppc-dev@...abs.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: pte_offset_map for ppc assumes HIGHPTE

On Thu, 2007-07-26 at 01:18 +0200, Andreas Schwab wrote:
> Satya <satyakiran@...il.com> writes:
> 
> > hello,
> > The implementation of pte_offset_map() for ppc assumes that PTEs are
> > kept in highmem (CONFIG_HIGHPTE). There is only one implmentation of
> > pte_offset_map() as follows (include/asm-ppc/pgtable.h):
> >
> > #define pte_offset_map(dir, addr)               \
> >          ((pte_t *) kmap_atomic(pmd_page(*(dir)), KM_PTE0) + pte_index(addr))
> >
> > Shouldn't this be made conditional according to CONFIG_HIGHPTE is
> > defined or not
> 
> kmap_atomic is always defined with or without CONFIG_HIGHPTE.
> 
> > (as implemented in include/asm-i386/pgtable.h) ?
> 
> I don't think that needs it either.

Depends... if you have CONFIG_HIGHMEM and not CONFIG_HIGHPTE, you are wasting
time going through kmap_atomic unnecessarily no ? it will probably not do anything
because the PTE page is in lowmem but still...

Ben.

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